Hafnium silicide target for forming gate oxide film and method for preparation thereof

ABSTRACT

The present invention relates to a hafnium silicide target for forming a gate oxide film composed of HfSi 1.02-2.00 . Obtained is a hafnium silicide target superior in workability and embrittlement resistance, and suitable for forming a HfSiO film and HfSiON film that may be used as a high dielectric gate insulation film in substitute for a SiO 2  film, and to the manufacturing method thereof.

TECHNICAL FIELD

[0001] The present invention relates to a hafnium silicide targetsuperior in workability and embrittlement resistance, and suitable forforming a HfSiO film and HfSiON film that may be used as a highdielectric gate insulation film, and to the manufacturing methodthereof. Moreover, the unit of “ppm” as used in this description shallmean wtppm in all cases.

BACKGROUND ART

[0002] The film thickness of a dielectric gate insulation film largelyinfluences the performance of a MOS transistor, and it is essential thatthe interface with the silicon substrate is electrically smooth and thatthe mobility of the carrier does not deteriorate.

[0003] Conventionally, a SiO₂ film has been used as this gate insulationfilm, and was the most superior in terms of interfacial quality. Inaddition, there is a characteristic in that the thinner the SiO₂ filmused as this gate insulation film, the number of carriers (that is,electrons or electron holes) increases, and the drain current alsoincreases thereby.

[0004] From the foregoing circumstances, each time the power supplyvoltage would decrease as a result of miniaturizing the wiring, the gateSiO₂ film has been consistently formed as thin as possible within arange that would not deteriorate the reliability of dielectricbreakdown. Nevertheless, a tunnel leakage current flows directly whenthe gate SiO2 ₂ film is formed of a thickness of 3 nm or less, and aproblem arises in that this film would not function as an insulationfilm.

[0005] Meanwhile, although attempts are being made to miniaturize thetransistor, so as long as there are limitations in the film thickness ofthe Sio₂ film, which is the gate insulation film as described above,miniaturization of the transistor loses its significance, and a problemarises in that the performance is not improved.

[0006] Moreover, in order to lower the power supply voltage of the LSIas well as lower the power consumption, it is necessary to make the gateinsulation film even thinner. Nevertheless, since there is a problemregarding the gate dielectric breakdown when the film thickness of theSiO₂ film is made 3 nm or less as described above, thinning of the filmhad a limitation in itself.

[0007] In light of the foregoing circumstances, a high dielectric gateinsulation film is being considered lately as a substitute for the SiO₂film. And, the HfSiO film and HfSiON film are attracting attention asthis type of high dielectric gate insulation film.

[0008] This high dielectric gate insulation film is a comparativelythick film, and is capable of acquiring a capacity equivalent to theSiO₂ film, and is characterized in that it is able to suppress thetunnel leakage current. Further, since this can be deemed as a film inwhich SiO₂ is added to Hf, interfacial quality similar to that of SiO₂can be expected.

[0009] Thus, sought is a sputtering target capable of easily and stablyforming a high-grade HfSiO and HfSiON high dielectric gate insulationfilm.

DISCLOSURE OF THE INVENTION

[0010] In order to overcome the foregoing problems, the presentinvention aims to provide a hafnium silicide target superior inworkability and embrittlement resistance, and suitable for forming aHfSiO film and HfSiON film that may be used as a high dielectric gateinsulation film in substitute for a SiO₂ film, and the manufacturingmethod thereof.

[0011] The present invention provides:

[0012] 1. A hafnium silicide target for forming a gate oxide filmcomposed of HfSi_(1.02-2.00)(In this composition ratio, however, Si:1.02 is not included. In other words, this implies that only the lowerlimit value of Si is 1.02 (or more). This applies throughout thisdescription.);

[0013] 2. A hafnium silicide target for forming a gate oxide filmcomposed of HfSi_(1.02-2.00) and containing a mixed phase principallyincluding a HfSi phase and a HfSi₂ phase;

[0014] 3. A hafnium silicide target for forming a gate oxide filmaccording to paragraph 1 or paragraph 2 above, characterized in that therelative density is 95% or more;

[0015] 4. A hafnium silicide target for forming a gate oxide filmaccording to each of paragraphs 1 to 3 above, characterized in that theoxygen content is 500 to 10000 ppm;

[0016] 5. A hafnium silicide target for forming a gate oxide filmaccording to each of paragraphs 1 to 4 above, characterized in that thezirconium content is 2.5 wt % or less;

[0017] 6. A hafnium silicide target for forming a gate oxide filmaccording to each of paragraphs 1 to 5 above, characterized in that theimpurities are C: 300 ppm or less, Ti: 100 ppm or less, Mo: 100 ppm orless, W: 10 ppm or less, Nb: 10 ppm or less, Fe: 10 ppm or less, Ni: 10ppm or less, Cr: 10 ppm or less, Na: 0.1 ppm or less, K: 0.1 ppm orless, U: 0.01 ppm or less, and Th: 0.01 ppm or less;

[0018] 7. A hafnium silicide target for forming a gate oxide filmaccording to each of paragraphs 1 to 6 above, characterized in that theaverage grain size is 5 to 200 μm;

[0019] 8. A manufacturing method of a hafnium silicide target forforming a gate oxide film, characterized in that the powder of thecomposition composed of HfSi_(1.02-2.00) is synthesized, pulverized tobe 100 mesh or less, and thereafter hot pressed at 1400° C. to 1535° C.;and

[0020] 9. A manufacturing method of a hafnium silicide target forforming a gate oxide film according to paragraph 8 above, characterizedin that hot pressing is performed at 150 to 2000 kgf/cm².

MODE FOR CARRYING OUT THE INVENTION

[0021] A high dielectric gate insulation film comprising the quality asa substitute for the SiO₂ film is formed by performing oxygen reactivesputtering to a HfSi target. This oxide film is considered to be ahybridization of an oxide film as represented with HfO₂* SiO₂ or a filmin which a part of the oxygen is replaced with nitrogen, and a targetwas usually demanded of a composition of Si/Hf=1.0. Generally, althoughthe composition ratio of Hf and Si is demanded to be a composition ratioclose to the target film, a Hf-rich oxide film tends to have a highrelative dielectric constant, a Si-rich oxide film has favorablecompatibility with a Si substrate and can easily become an amorphousstructure, and therefore possesses a characteristic of having a low leakcurrent.

[0022] In light of the above, it is necessary to consider and determinethe balance of the dielectric constant and leak current in accordancewith the purpose of use. Moreover, each manufacturing process of adevice is demanded of unique compatibility, and a material capable ofarbitrarily changing the composition ratio of Hf and Si as necessary isin demand.

[0023] When sintering the mixed powder of hafnium and silicon, inaccordance with the composition ratio, silicide phases such as a HfSiphase and HfSi₂ phase, and mixed crystals such as a Hf phase and Siphase are formed, but generally speaking, there is a problem in thatthese hafnium silicide inter compounds are not able to obtain sufficientdensity increase during the sintering since they have a high meltingpoint, become a sintered body of a porous texture, and thereafter becomea target with numerous generation of particles.

[0024] And, unless adjusting the hot pressing conditions; that is, theheating temperature and pressure in accordance with the compositionratio, a target of an optimum density cannot be obtained.

[0025] Upon persevering to improve the increase in density, the presentinvention succeeded in obtaining a target suitable as a hafnium silicidetarget for forming a gate oxide film.

[0026] The present invention provides a hafnium silicide target forforming a gate oxide film composed of HfSi_(1.02-2.00) in considerationof the balance between the dielectric constant and leak current. Thishafnium silicide target comprises a mixed phase having a HfSi phase anda HfSi2 phase as principal phases, which eliminates the porousstructure, and which has a relative density of 95% or more.

[0027] When the relative density becomes less than 95%, the brittlenessdeteriorates due to the lack of density, and the workability alsodeteriorates thereby. This also generates the increase of particlescaused by the fracture and scattering of fragile crystals. It istherefore preferable that the relative density be within the foregoingrange.

[0028] It is desirable that the oxygen content within the hafniumsilicide target for forming the gate oxide film be 500 to 10000 ppm.When oxygen is less than 500 ppm, there is a possibility that the targetwill ignite during the manufacture thereof, and, contrarily, when oxygenexceeds 10000 ppm, oxygen within the target will deposit as an oxide andcause abnormal discharge during the sputtering, particles will increasethereby, and the product yield rate will decrease as a result thereof.

[0029] Further, it is preferable that the zirconium content within thetarget be controlled to 2.5 wt % or less. When the amount of zirconiumexceeds 2.5 wt %, process conditions such as voltage, current andsubstrate temperature during the reactive sputtering for forming theoxide film will vary greatly, and this is not preferable.

[0030] Moreover, it is preferable that impurities within the hafniumsilicide target for forming the gate oxide film are C: 300 ppm or less,Ti: 100 ppm or less, Mo: 100 ppm or less, W: 10 ppm or less, Nb: 10 ppmor less, Fe: 10 ppm or less, Ni: 10 ppm or less, Cr: 10 ppm or less, Na:0.1 ppm or less, K: 0.1 ppm or less, U: 0.01 ppm or less, and Th: 0.01ppm or less. This is because these impurities will become thecontamination source to the gate electrode and lower Si substrate.

[0031] In order to manufacture a hafnium silicide target for forming agate oxide film superior in embrittlement resistance composed ofHfSi_(1.02-2.00), powder of the composition composed of HfSi_(1.02-2.00)is combined and thereafter hot pressed at 1400° C. to 1535° C. If thetemperature is less than 1400° C., the density will be insufficient, andif the temperature exceeds 1535° C., this is not preferable sincepartial dissolution will begin to occur.

[0032] Upon combining the powder of the composition composed ofHfSi_(1.02-2.00), hafnium hydride powder and Si powder are prepared andmixed at a molar ratio of 1:1.02 to 1:2.00, and thereafter sintered at600° C.-800° C.

[0033] Although the use of Hf powder may also be considered, Hf powderis not preferable since it has strong oxidizability, and, whenpulverized, there is a problem in that it may ignite.

[0034] Therefore, hafnium hydride is used for preventing this kind ofignition. It is desirable that hafnium hydride powder and silicon powderare used upon being pulverized under 100 mesh. The use of this finepowder enables the realization of high density at the time of sintering.

[0035] Dehydrogenation and silicide formation are conducted with theheating process during the sintering described above. Dehydrogenationbegins to occur from around 600° C. Although sintering is conducted in avacuum (1×10⁻⁴ to 1×10⁻² Torr), it becomes a slight hydrogen atmospherefor dehydrogenation.

[0036] Moreover, dehydrogenation is completed upon heating to atemperature of 800° C., and, the portion that may ignite with the Hfmetal is formed into a silicide, or sintered to a degree without anyfear of ignition (approximately 3 μm or larger).

[0037] As described above, by conducting dehydrogenation and forming asilicide at a low temperature during the thermal synthesis, grain growthcan be suppressed, primary grain of the sintered powder remains fine,and may be made into a high density during molding. If the sinteredpowder becomes coarse, pulverization before sintering becomes difficult,and results in residual coarse particles and deterioration in density.

[0038] Accordingly, a significant characteristic is yielded in that thecrystal grain growth can be suppressed since sintering is conducted at alow temperature, and the average crystal grain size of the hafniumsilicide target for forming a gate oxide film can be made to be 5 to 200μm. And, high densification can be achieved upon sintering.

[0039] With a target having an average crystal grain size of less than 5μm, it is difficult to make the amount of oxygen 10000 ppm or less, andthere is fear of ignition during the manufacturing process. Moreover,when the average crystal grain size exceeds 200 μm, since particles willincrease and the production yield rate will deteriorate, it is desirablethat the average crystal grain size be set between 5 and 200 μm asdescribed above.

[0040] High densification during sintering is enabled through thesynthesis of the powder composed from the foregoing HfSi_(1.02-2.00) andhot pressing this at 1400° C. to 1535° C.

[0041] The foregoing hot pressing temperature is a temperatureimmediately under the liquid phase generation of the synthesized powder,and this temperature range is important for the sintering. This enablesthe realization of a high density hafnium silicide target having arelative density of 95% or more.

[0042] The high density hafnium silicide target of the present inventionyields an effect in preventing the generation of particles caused by thepores during sputtering.

EXAMPLES

[0043] Next, the Examples are explained. Further, these Examples aremerely illustrative, and the present invention shall in no way belimited thereby. In other words, the present invention shall include allother modes or modifications other than these Examples within the scopeof the technical spirit of this invention.

Example 1

[0044] A synthesized powder of HfSi_(1.1) was obtained by mixing HfH₂powder under 100 mesh and Si powder under 100 mesh and heating this at800° C. in a vacuum, whereby dehydrogenation reaction and silicidesynthetic reaction were conducted at once.

[0045] This hafnium silicide powder was pulverized to obtain hafniumsilicide powder under 100 mesh. Here, it is also possible to addpre-synthesized hafnium silicide powder. It has been confirmed with XRDthat this hafnium silicide powder is composed of a mixed phase includinga HfSi phase and HfSi₂ phase.

[0046] A sintered body having a density of 99.3% was obtained by hotpressing this silicide powder under the condition of 300 kg/cm²×2 hoursat 1500° C. This was further machine processed to prepare a target of φ300 mm×6.35 mmt. Texture with hardly any pores was obtained thereby.

[0047] Sputtering was performed with the target prepared as describedabove, and, upon measuring the particles on a 6 inch wafer, only a totalof 12 particles having a measurement of 0.2 μm or larger were found, andthe generation of particles decreased considerably.

[0048] A hafnium silicide target superior in workability andembrittlement resistance was obtained as a result of the above. Further,since this target may be employed in wet processing, there is no longerany fear of ignition during the processing.

Example 2

[0049] A synthesized powder of HfSi_(1.5) was obtained by mixing HfH₂powder under 100 mesh and Si powder under 100 mesh and heating this at800° C. in a vacuum, whereby dehydrogenation reaction and silicidesynthetic reaction were conducted at once.

[0050] This silicide powder was pulverized to obtain hafnium silicidepowder under 100 mesh. Here, it is also possible to add pre-synthesizedhafnium silicide powder. It has been confirmed with XRD that thishafnium silicide powder is composed of a mixed phase including a HfSiphase and HfSi₂ phase.

[0051] A sintered body having a density of 99.8% was obtained by hotpressing this hafnium silicide powder under the condition of 300kg/cm²×2 hours at 1420° C. This was further machine processed to preparea target of φ 300 mm×6.35 mmt.

[0052] Sputtering was performed with the hafnium silicide targetprepared as described above, and, upon measuring the particles on a 6inch wafer, only a total of 18 particles having a measurement of 0.2 μmor larger were found, and the generation of particles decreasedconsiderably.

[0053] A hafnium silicide target superior in workability andembrittlement resistance was obtained as a result of the above. Further,there is no fear of ignition during the processing.

Example 3

[0054] A synthesized powder of HfSi_(1.9) was obtained by mixing HfH₂powder under 100 mesh and Si powder under 100 mesh and heating this at800° C. in a vacuum, whereby dehydrogenation reaction and silicidesynthetic reaction were conducted at once.

[0055] This silicide powder was pulverized to obtain hafnium silicidepowder under 100 mesh. Here, it is also possible to add pre-synthesizedhafnium silicide powder. It has been confirmed with XRD that thishafnium silicide powder is composed of a mixed phase including a HfSiphase and HfSi₂ phase.

[0056] A sintered body having a density of 98.4% was obtained by hotpressing this hafnium silicide powder under the condition of 300kg/cm²×2 hours at 1520° C. This was further machine processed to preparea target of φ 300 mm×6.35 mmt.

[0057] Sputtering was performed with the hafnium silicide targetprepared as described above, and, upon measuring the particles on a 6inch wafer, only a total of 20 particles having a measurement of 0.2 82m or larger were found, and the generation of particles decreasedconsiderably.

[0058] A hafnium silicide target superior in workability andembrittlement resistance was obtained as a result of the above. Further,there is no fear of ignition during the processing.

Comparative Example 1

[0059] A synthesized powder of HfSi_(1.3) was obtained by mixing HfH₂powder under 100 mesh and Si powder under 100 mesh and heating this at800° C. in a vacuum, whereby dehydrogenation reaction and silicidesynthetic reaction were conducted at once. This silicide powder waspulverized to obtain hafnium silicide powder under 100 mesh. It has beenconfirmed with XRD that this hafnium silicide powder is composed of amixed phase including a HfSi phase and HfSi₂ phase.

[0060] A sintered body was obtained by hot pressing this silicide powderunder the condition of 120 kg/cm²×2 hours at 1500° C. The obtainedsintered body had a low density of 92.7%. This was further machineprocessed to prepare a target of φ 300 mm×6.35 mmt.

[0061] Since the density of this target is low, through-pores existed.Therefore, since it is extremely difficult to eliminate contamination ofthe working fluid during the processing upon manufacturing the targetemployed in manufacturing the actual device, it is not possible toperform wet processing. Therefore, in order to prevent ignition of theprocessing powder, special measures must be taken such as performing dryprocessing under an inert gas atmosphere.

[0062] Sputtering was performed with the target prepared as describedabove, and, upon measuring the particles on a 6 inch wafer, a total of270 particles having a measurement of 0.2 μm or larger were found. Inaddition, a plurality of protrusions referred to as nodules hadgenerated on the outer peripheral face of the target.

[0063] As described above, density cannot be improved when sintering athigh temperatures outside the scope of the present invention, and thisalso resulted in the generation of numerous particles.

Comparative Example 2

[0064] A synthesized powder of HfSi_(1.3) was obtained by mixing HfH₂powder under 100 mesh and Si powder under 100 mesh and heating this at800° C. in a vacuum, whereby dehydrogenation reaction and silicidesynthetic reaction were conducted at once.

[0065] This silicide powder was pulverized to obtain hafnium silicidepowder under 100 mesh. It has been confirmed with XRD that this hafniumsilicide powder is composed of a mixed phase including a HfSi phase andHfSi₂ phase.

[0066] A sintered body was obtained by hot pressing this hafniumsilicide powder under the condition of 300 kg/cm²×2 hours at 1380° C.The obtained sintered body had a low density of 90.6%. This was furthermachine processed to prepare a target of φ 300 mm×6.35 mmt.

[0067] Since the density of this target is low, through-pores existed.Therefore, since it is extremely difficult to eliminate contamination ofthe working fluid during the processing upon manufacturing the targetemployed in manufacturing the actual device, it is not possible toperform wet processing. Therefore, in order to prevent ignition of theprocessing powder, special measures must be taken such as performing dryprocessing under an inert gas atmosphere.

[0068] Sputtering was performed with the target prepared as describedabove, and, upon measuring the particles on a 6 inch wafer, a total of490 particles having a measurement of 0.2 μm or larger were found. Inaddition, a plurality of nodules had generated.

[0069] As described above, density cannot be improved when sintering atlow temperatures outside the scope of the present invention, and thisalso resulted in the generation of numerous particles.

[0070] The relative density of the respective targets in Examples 1 to 3was 95% or more. Further, the number of particles was 20 or less.Improvement in the relative density was achieved similarly under the hotpressing conditions of 1400° C. to 1535° C.

[0071] As described above, it has been confirmed that a hafnium silicidetarget in which the Hf:Si ratio is 1:1.02 to 2.00 can be stablymanufactured under the foregoing conditions while improving the densityof the sintered body.

[0072] Contrarily, the relative density in Comparative Example 1 was lowat 92.7%. The result was inferior where the number of particles was 270and nodules arose as a result thereof.

[0073] Moreover, the relative density in Comparative Example 2 was lowat 90.6%. The result was inferior where the number of particles was 490and nodules similarly arose as a result thereof.

[0074] Accordingly, superiority of the Examples according to the presentinvention is evident, and it is further clear that the present inventionpossesses superior characteristics.

[0075] Effect of the Invention

[0076] The present invention is characterized in that it is able toobtain a hafnium silicide target superior in workability andembrittlement resistance, and suitable for forming a HfSiO film andHfSiON film that may be used as a high dielectric gate insulation filmin substitute for a SiO₂ film.

[0077] The present hafnium silicide target has a relative density of 95%or more and is of high density, and possesses superior strength.

[0078] Moreover, the highly densified silicide target of the presentinvention is capable of preventing the generation of particles arisingfrom pores during the sputtering and the generation of particlesresulting from the fracture and scattering of brittle textures, andyields a significant advantage in that it does not ignite during theprocessing or manufacturing process of the target.

1. A hafnium silicide sintered target for forming a gate oxide filmcharacterized in that composed of HfSi_(1.02-2.00), containing a mixedphase principally including a HfSi phase and a HfSi₂ phase, and therelative density is 95% or more.
 2. (Delete)
 3. (Delete)
 4. A hafniumsilicide sintered target for forming a gate oxide film according toclaim 1, characterized in that the oxygen content is 500 to 10000 ppm.5. A hafnium silicide sintered target for forming a gate oxide filmaccording to claim 1 or claim 4, characterized in that the zirconiumcontent is 2.5 wt % or less.
 6. A hafnium silicide sintered target forforming a gate oxide film according to each of claims 1, 4 and 5,characterized in that the impurities are C: 300 ppm or less, Ti: 100 ppmor less, Mo: 100 ppm or less, W: 10 ppm or less, Nb: 10 ppm or less, Fe:10 ppm or less, Ni: 10 ppm or less, Cr: 10 ppm or less, Na: 0.1 ppm orless, K: 0.1 ppm or less, U: 0.01 ppm or less, and Th: 0.01 ppm or less.7. A hafnium silicide sintered target for forming a gate oxide filmaccording to each of claims 1 and 4 to 6, characterized in that theaverage grain size is 5 to 200 μm.
 8. A manufacturing method of ahafnium silicide sintered target for forming a gate oxide filmcharacterized in that the powder of the composition composed ofHfSi_(1.02-2.00) is synthesized, pulverized to be 100 mesh or less, andthereafter hot pressed at 1400° C. to 1535° C.
 9. A manufacturing methodof a hafnium silicide sintered target for forming a gate oxide filmaccording to claim 8, characterized in that hot pressing or hotisostatic pressing (HIP) is performed at 150 to 2000 kgf/cm².